Understanding the type, formation energy and capture cross section of defects is one of the challenges in the field of organometallic halide perovskite (OMHP) devices. Currently, such understanding is limited, restricting the power conversion efficiencies of OMHP solar cells from reaching their Shockley–Queisser limit. In more mature semiconductors like Si, the knowledge of defects is one of the major factors in successful technological implementation. This knowledge and its control can make a paradigm shift in the development of OMHP devices. Here, we report on deep level (DL) defects and their effect on the free charge transport properties of the single crystalline methylammonium lead bromide (MAPbBr₃) perovskite. To determine DL activation energy and capture cross section, we used photo-Hall effect spectroscopy (PHES) with enhanced illumination in both steady-state and dynamic regimes. This method has shown to be convenient due to the direct DL visualization by sub-bandgap photo-excitation of trapped carriers. DLs with activation energies of E_V + 1.05 eV, E_V + 1.5 eV, and E_V + 1.9 eV (or E_C − 1.9 eV) were detected. The hole capture cross section of σ_h = 4 × 10⁻¹⁷ cm² is found using photoconductivity relaxation after sub-bandgap photo-excitation. Here, our experimental results demonstrate the existence of DL defects responsible for non-radiative recombination and their positions inside the bandgap for the first time. Additionally, the transport properties of single crystal MAPbBr₃ are investigated by Time of Flight (ToF) measurements at several biases. These measurements further confirm the increase of Hall mobility and the enhancement of hole transport produced by sub-bandgap illumination in MAPbBr₃ devices. The analysis of charge carrier transport by ToF measurements in combination with the energy of DLs identified by PHES can explain the long hole carrier lifetime in MAPbBr₃ devices, while the electron carrier lifetime is largely affected by trap-assisted recombination. Here, our studies provide strong evidence for deep levels in OMHPs and open a richer picture of the role and properties of deep levels in MAPbBr₃ single crystals as a system model for the first time. The deeper knowledge of the electronic structure of OMHPs could open further opportunities in the development of more feasible technologies. Indeed, knowledge of the exact positions of DLs is beneficial in controlling these defects by crystal growth modification to eliminate these defects as was done for classical inorganic semiconductors, for example, in Si, GaAs, and CdTe development.

The charge-transport properties of semiconductor and semiinsulator materials are strongly controlled by the crystallographic defects manifesting energy states in the bandgap. In this paper, we study deep levels (DLs) in p-type ${\mathrm{Cd}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ by photo-Hall-effect spectroscopy with enhanced illumination. We show that the mobility of minority ($925\pm 11{\mathrm{cm}}^2{\mathrm{s}}^{-1}{\mathrm{V}}^{-1}$) and majority ($59.6\pm 0.4{\mathrm{cm}}^2{\mathrm{s}}^{-1}{\mathrm{V}}^{-1}$) carriers can be deduced directly from the spectra by using proper wavelength and excitation intensity. Four deep levels with ionization energies $E_{t1}=E_V+0.63\mathrm{eV}$, $E_{t2}=E_V+0.9\mathrm{eV}$, $E_{t3}=E_C-1.0\mathrm{eV}$, and $E_{t4}=E_C-1.3\mathrm{eV}$ are detected and their positions in the bandgap are verified by comparison of photogenerated electron and hole concentrations. The deduced DL model is analyzed by numerical simulations with Shockley-Reed-Hall charge generation-recombination theory and compared with alternative DL models differing in the position of selected DLs relative to $E_C$ and $E_V$. We show that the consistent explanation of collected experimental data principally limits the applicability of alternative DL models. We also demonstrate the importance of the extended operation photon fluxes ($I>4\times {10}^{14}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$) used in the spectra acquisition for correct determination of DL character. Negative differential photoconductivity is observed and studied by charge dynamic theoretical simulations.

High resistive CdTe and CdZnTe single crystals were measured by photo-Hall effect spectroscopy (PHES) and photoluminescence spectroscopy (PL) with the aim of discovering the position of deep levels (DLs) in the band gap. Illumination in the range of 0.65–1.77 eV, room temperature, and DC electrical measurements were used in the case of PHES. Low temperature (4 K) photoluminescence spectra were recorded in the spectral range above 0.47 eV. Eight samples, both n -type and p -type, were studied and typical shapes of spectra were collected, compared and interpreted for both spectroscopy methods. It was shown that a simple single-level model of PHES often fails in the interpretation of DLs distant from the midgap. Eight DLs with the energy E _c − 0.65 eV, E _c − 0.8 eV, E _c − 0.9 eV, E _c − (1.10–1.15) eV, E _v + 0.70 eV, E _v + 0.85 eV, E _v + 1.0 eV, and E _c − 1.25 eV were interpreted. A memory effect characterized by a relaxation time of about 60 s was observed at the 0.8 eV level and allowed us to determine the 1.7 × 10 ⁻¹⁷ cm ² capture cross-section of electrons on this level. It is argued that PHES is a convenient complementary method to identify and characterize DLs, including DLs inaccessible by thermal emission techniques. DLs observed by PHES were consistently verified by PL.

Photo-Hall effect spectroscopy was used in the study of deep levels in high resistive CdZnTe. The monochromator excitation in the photon energy range 0.65–1.77 eV was complemented by a laser diode high-intensity excitation at selected photon energies. A single sample characterized by multiple unusual features like negative differential photoconductivity and anomalous depression of electron mobility was chosen for the detailed study involving measurements at both the steady and dynamic regimes. We revealed that the Hall mobility and photoconductivity can be both enhanced and suppressed by an additional illumination at certain photon energies. The anomalous mobility decrease was explained by an excitation of the inhomogeneously distributed deep level at the energy Ev + 1.0 eV, thus enhancing potential non-uniformities. The appearance of negative differential photoconductivity was interpreted by an intensified electron occupancy of that level by a direct valence band-to-level excitation. Modified Shockley-Read-Hall theory was used for fitting experimental results by a model comprising five deep levels. Properties of the deep levels and their impact on the device performance were deduced.

The performance of the CdTe radiation detectors heavily relies on the method of contact preparation. A convenient research method addressing this problem is the laser-induced transient current technique. In this paper, we compare the performance of two CdTe crystals which underwent different metallization processes. We showed that appropriately designed Au/Al contacts induce much less bulk polarization than commercial Pt/In electrodes under the same working conditions and can thus provide a convenient alternative to the industry standard. The comparison was based on the monitoring of the time-dependent sensor polarization measuring transient currents excited by above-bandgap laser illumination complemented by the Am 241 gamma spectroscopy. The theoretical analysis of current waveforms and radiation spectra enabled us to determine the charge carrier mobility, mobility-lifetime products of electrons and holes, and temporal and bias dependence of the space charge formation.